1. M. Yoda, S. I. Abdel-Khalik, D. L. Sadowski and M. D. Hageman Woodruff School of Mechanical Engineering Update on Thermal Performance of the Gas- Cooled Plate-Type Divertor

2. ARIES-Pathways (8/09) 2 Objective / Motivation Objective Experimentally evaluate and validate thermal performance of gas-cooled divertor designs in support of the ARIES team Motivation Leading divertor designs rely on jet impingement cooling to achieve desired performance Accommodate heat fluxes up to 10 MW/m 2 Performance is “robust” with respect to manufacturing tolerances and variations in flow distribution Extremely high heat transfer coefficients (~50 kW/(m 2  K)) predicted by commercial CFD codes used for the design Experimentally validate such numerical predictions

3. ARIES-Pathways (8/09) 3 Approach Design and instrument test modules that closely match divertor geometries Conduct experiments at conditions matching and spanning expected non-dimensional parameters for prototypical operating conditions – Reynolds number Re – Use air instead of He Measure temperature distributions and pressure drop Compare experimental data with predictions from CFD software for test geometry and conditions – Nu(Re),  P * (Re)

4. ARIES-Pathways (8/09) 4 Investigated leading gas-cooled divertor designs FZK Helium-Cooled Multi-Jet (HEMJ) “Finger” [Norajitra et al. 2005] – Ihli et al. 2007; Crosatti et al. 2009 ARIES-CS T-Tube [Ihli et al. 2007; Raffray et al. 2008] – Crosatti et al. 2007; Abdel-Khalik et al. 2008; Crosatti et al. 2009 ARIES-Pathways Plate-Type Design [Malang; Wang et al. 2009] – Variant with metal open-cell foam: Gayton et al. 2009 [Sharafat et al. 2007] – Variant with pin-fin array: In progress Some History

5. ARIES-Pathways (8/09) 5 Outcomes Enhanced confidence in predicted performance by commercial CFD codes at prototypical and off- normal operating conditions – FLUENT ® Use validated CFD codes to optimize/modify divertor designs Predict sensitivity to changes in geometry and operating conditions to define and establish manufacturing tolerances

6. ARIES-Pathways (8/09) 6 Plate-Type Divertor Design Covers large area (2000 cm 2 = 0.2 m 2 ): divertor area O(100 m 2 ) 100 cm Castellated W armor 0.5 cm thick 20 – HEMJ, T-tube cool 2.5, 13 cm 2 – Accommodates up to 10 MW/m 2 without exceeding T max  1300 °C,  max  400 MPa – 9 individual manifold units with ~3 mm thick W-alloy side walls brazed together

7. ARIES-Pathways (8/09) 7 GT Test Module Armor In Out Jet issues from 0.5 mm slot, then impinges on and cools underside of W-alloy pressure boundary – Coolant flows along 2 mm gap, exits via outlet manifold – Original design [Malang 2007] – Use air as coolant – Reynolds number Re = 1.1  10 4 – 6.8  10 4 (vs. 3.3  10 4 at nominal operating conditions) – Nominal heat flux q  nom = 0.2– 0.75 MW/m 2 In Out Heated brass shell Al inner cartridge

8. ARIES-Pathways (8/09) 8 Modified Manifold Design To reduce thermal stress, current modified design adds [Wang et al. 2009] – 2 mm stagnant He region outside outlet manifold – 8 mm thick W-alloy base 2.2 cm In Out Armor W-alloy

9. ARIES-Pathways (8/09) 9 Al Inner Cartridge In Out Inlet, outlet manifolds embedded inside Al cartridge – Manifolds 19 mm  15 mm  76.2 mm – 2 mm  76.2 mm slot – Coolant enters outlet manifold via holes – Side wall bolted on

10. ARIES-Pathways (8/09) 10 Brass Outer Shell Models pressure boundary – 5 TC in shell to measure cooled surface temperature distribution: 2 in center; (1,5) and (3,4) at same depth 0.5 mm from surface – Brass shell heated by heater block – k for brass similar to that of W-alloy

11. ARIES-Pathways (8/09) 11 Pin-Fin Array Can thermal performance of leading divertor designs be further improved? – Mo open-cell foam in 2 mm gap increased HTC by 40–50%, but also increased  P * by similar fraction [Gayton et al. 2009] – In HEMP, a variant of HEMJ, coolant impinges on pin-fin array [Diegele et al. 2003] Combine plate with pin-fin array – 808  1.0 mm  2.0 mm pin fins (nearly) contacting Al cartridge on 1.2 mm pitch – 2 mm “clear” area for impinging jet – Pin fins EDM’ed into inside of brass shell

12. ARIES-Pathways (8/09) 12 Heated Test Section Copper heater block Graphite shim Brass outer shell Aluminum cartridge Gasket

13. ARIES-Pathways (8/09) 13 GT Air Flow Loop Inlet P, T measurement Outlet P, T measurement Cu heater block 3 cartridge heaters 6 TC in neck measure q  2 TC at top monitor max. Cu temperature

14. ARIES-Pathways (8/09) 14 Nu from TC data – Nearly uniform T along slot – Nu based on gap width, k at 300K and effective HTC (for pin fins) q  nom = 0.2–0.75 MW/m 2 Effect of Pin Fins Re (/10 4 ) Pin fins Bare surface  TC 1  TC 4  TC 2  TC 5  TC 3 Nominal operating condition Nu

15. ARIES-Pathways (8/09) 15 Ratio of Nu and  P for cooled surface with, without pin-fins Pin-fins with ~260% more surface area improve cooling performance by ~150%–200% while increasing pressure drop by ~40–70% Comparison: Pins vs. Bare Re (/10 4 ) Nu p / Nu Mass flow rate [g/s] Pp* / P *Pp* / P * Nominal operating condition

16. ARIES-Pathways (8/09) 16 Summary Designed and studied experimental test modules modeling leading He-cooled divertor designs – T-tube, HEMJ “ finger, ” plate – Conducted dynamically similar thermal-hydraulics experiments matching and spanning expected prototypical operating conditions Used commercial CFD software to predict performance of experimental test modules – Good agreement between experimental data and model predictions (including those from other groups) – Use validated codes to predict performance of gas-cooled components with complex geometries

17. ARIES-Pathways (8/09) 17 Conclusions Plate-type divertor + pin-fin array promising design – Smaller number of divertor modules required  reduced cost, complexity – Two- to three-fold enhancement by pin fins  can accommodate heat fluxes much higher than 10 MW/m 2 Initial results for un-optimized configuration: use CFD to suggest improvements to current experimental design – Effect of pin pitch, diameter – Effect of slot width

18. ARIES-Pathways (8/09) 18 Next Steps To complete ARIES-Pathways study: Validate CFD codes (e.g. FLUENT) and plate models with experimental data – Model pin-fin array Use validated CFD codes to optimize/modify pin-fin layout – Predict maximum heat flux that can be accommodated by optimized pin-fin/plate-type divertor – Predict pressure drop across optimized pin-fin array